Polysulfone membrane and method for its manufacture

ABSTRACT

A synthetic membrane consisting of a mixture of polysulfone and sulfonated polysulfone and not more than 20 wt. % of other polymers, characterized in that the mixture contains 0.5 to 8 wt. % sulfonated polysulfone, possibly as the salt of sulfonic acid, and a method for manufacturing this synthetic membrane, characterized in that one or more solvents are added to a mixture composed of 0.5 to 8 wt. % sulfonated polysulfone, possibly as the salt of sulfonic acid, polysulfone and not more than 20 wt. % of other polymers, the mixture is dissolved to form a polymer solution, the latter is shaped, and precipitated to form a membrane in a precipitating bath by means of one or more precipitating agents.

FIELD OF THE INVENTION

The invention relates to a synthetic membrane consisting of a mixture ofpolysulfone and sulfonated polysulfone and no more than 20 wt. % ofother polymers. The invention likewise relates to a method formanufacturing this synthetic membrane.

BACKGROUND

Synthetic membranes and separating processes based on them have beenknown for a long time. In addition to classical applications, forexample, seawater desalination using reverse osmosis or ultrafiltrationof process water from electrophoretic dip painting to recover the paint,membrane processes are becoming increasingly important in the areas offood technology, medicine, and pharmacy. In the latter cases, membraneseparating processes have the great advantage that the materials to beseparated are not subjected to thermal stress or even damaged.

Often, an important prerequisite for the usability of membranes in theseareas is the sterilizability of the membrane. For safety and ecologicalreasons at least, steam sterilization is preferred over chemicalsterilization, for example, using ethylene oxide, or sterilization byradiation, especially by gamma radiation.

Steam sterilization normally involves a half-hour treatment of themembrane or membrane system with hot steam at temperatures in excess of110° C. Thus, the criterion of steam sterilizability severely limits thenumber of potential membrane materials. Thus, for example, membranesmade of polyacrylonitrile are basically not steam-sterilizable becauseexceeding the glass temperature of the polymer results in anirreversible damage to the material and/or the membrane. In addition,hydrolysis-sensitive polymers, for example, certain polycarbonates andpolyamides, cannot withstand hot steam sterilization unscathed.

Steam-sterilizable membranes made of polyether imides, polysulfones, orpolyvinylidene fluoride are known, for example. A major disadvantage ofthese membranes consists in the hydrophobic nature of the membranematerial, which prevents spontaneous wetting with aqueous media.Consequently, the membrane must be prevented from drying completely orthe membrane must be treated with a hydrophobic agent, glycerin, forexample, before drying.

Hydrophilic membranes are characterized by the fact that they arewettable with water. A measure of wettability is the wetting angle thata water drop forms with the surface of the membrane. In hydrophilicmaterials, this edge angle is always greater than 90°.Phenomenologically, the wetting of a dialysis membrane can also bedetected by the fact that a drop of water placed on the surface of themembrane penetrates the membrane after a short time.

Another serious disadvantage of hydrophobic materials consists in thefact that they often possess a powerful nonspecific adsorption capacity.Therefore, when hydrophobic membranes are used, frequently a rapid,closely adhering coating of the membrane surface with preferablyhigher-molecular-weight solution components takes place. Thisphenomenon, known as fouling, leads to a rapid deterioration of themembrane permeability. Subsequent treatment of the membrane with ahydrophilizing medium cannot prevent fouling in the long term.

Suggestions for hydrophilic membranes have already been proposed that donot suffer from these disadvantages. Thus, DE-OS 3,149,976 proposesusing a polymer mixture for making a hydrophilic membrane that containsat least 15 wt. % polyvinylpyrrolidone in addition to polysulfone orpolyamide. For hydrophilization of polyimide and polyether sulfonemembranes, for example, EP-A-0,228,072 claims the use of polyethyleneglycol in amounts from 44 to 70 wt. %, based on the polymer solution.

Hydrophilization of membranes by using large quantities of water-solublepolymers however has the disadvantage that the hydrophilic nature of themembrane constantly decreases when they are used in aqueous media, sincethe water-soluble polymer is washed out. This can create a situationsuch that the membrane material recovers its original hydrophobic natureand the negative accompanying phenomena associated with it and listedabove are exhibited.

EP-A-0,261,734 describes the hydrophilization of polyetherimidemembranes using polyvinylpyrrolidone. The polyvinylpyrrolidone iscrossed linked in the non-swollen state to prevent the washing outeffect. The membrane manufacturing process is very tedious and hencecost-intensive, since the solvent and precipitating agent must first beremoved from the membrane after precipitation and prior to crosslinking, but not the polyvinylpyrrolidone. It is only at this point thatthe cross linking of the polyvinylpyrrolidone is performed by using hightemperature, radiation, or chemically using isocyanates, whose residuesmust be absolutely completely removed before the membrane is used in thefood or medicine area.

The disadvantages described above can be avoided by using hydrophilic,yet water-insoluble, polymers for making the membranes. Thus, in anumber of patents, for example, EP-A-0,182,506 and U.S. Pat. No.3,855,122, the manufacture of membranes from sulfonated polymers isclaimed. The methods described in these patents however are onlysuitable for making flat membranes. The membranes possess a high saltretention capacity and are used primarily for reverse osmosis.

Another approach to hydrophilic membranes is proposed in U.S. Pat. No.4,207,182 and in two Japanese Disclosure documents (JP-OS 61-249,504 andJP-OS 62-49,912). According to these publications, hydrophilic membranesfor ultrafiltration of aqueous solutions can be advantageouslymanufactured from mixtures of sulfonated and nonsulfonated polysulfone.

An important goal of the invention described in U.S. Pat. No. 4,207,182is the use of highly concentrated polymer solutions to manufacturemembranes which nevertheless are characterized by a high hydraulicpermeability. This is accomplished by using polymer mixtures, with thepercentage of sulfonated polysulfone based on the total polymer mixtureof nonsulfonated and sulfonated polysulfone being between 10 and 30 wt.%.

A high hydraulic permeability however is not advantageous for allapplications. Thus, high hydraulic permeability in dialysis results inreverse filtration and hence to contamination of the liquid to bedialyzed with undesired materials from the dialysate.

As indicated by the examples in U.S. Pat. No. 4,207,182, the membranesaccording to the invention are also characterized by high screeningcoefficients for dextran with a molecular weight of 110,000 daltons.

In view of the high hydraulic permeability and the associated highpermeability for macromolecular substances with a molecular weightgreater than 100,000 daltons, the membranes resulting from the claimedpolymer mixtures are not suitable for hemodialysis. This is all the moreso when one considers that the dialytic permeability of the membranesmanufactured according to U.S. Pat. No. 4,207,182 is comparatively low.

U.S. Pat. No. 4,545,910 claims membranes that exhibit the performancedata of a conventional ultrafiltration membrane. The material for themembrane can be chosen from a plurality of substances, includingpolyacrylonitrile compounds.

In manufacturing synthetic non-cellulosic membranes, such as those frommaterials such as polyethersulfone, polyamide, or polyacrylonitrilecompounds, a number of properties of the material that play a role inthe future application of the material must be taken into account.

Thus, such a membrane, if it is to be used for dialysis, must exhibit orproduce histamine release which is as low as possible. Increasedhistamine release results in a series of unpleasant side effects indialysis patients, such as headache and pain in the limbs as well asother pain states that have a negative effect on the health of thepatient. The limiting value for histamine release of course must bedetermined individually for each person. This value depends on aplurality of factors (age, sex, weight, etc.) and therefore cannot bespecified generally.

Histamine is a highly active biological substance so that in any eventexcessive release should be avoided. Reference is made in thisconnection, for example, to papers by E. Neugebauer et al., BehringInst. Mitt., No. 68, 102-133 (1981) or W. Lorenz et al., Klin.Wochenschr. 60, 896-913 (1982).

A membrane of this kind should also exhibit values that are as low aspossible for bradykinin generation. Bradykinin generation is likewiselinked with unpleasant side effects that can pose a danger to dialysispatients (G. Bonner et al., J. of Cardiovasc. Pharm. 15 (Supplement 6),pp. 46-56 (1990). Even though the clinical significance of bradykiningeneration like that of histamine release has not yet been completelystudied, an attempt should be made to avoid whenever possible thisgeneration which can be triggered by a high percentage of sulfonatecompounds in the membrane through so-called "contact activation", duringdialysis.

SUMMARY OF THE INVENTION

Hence, a goal of the invention is to provide a membrane which issteam-sterilizable, exhibits a high degree of biocompatibility, and isalso outstandingly suited for use in the medical area because of itsseparating properties.

This and other goals are achieved by a synthetic membrane that iscomprised of a mixture of polysulfone and sulfonated polysulfone and notmore than 20 wt. % of other polymers, characterized by the fact that themixture contains 0.5 to 8 wt. % of sulfonated polysulfone, possibly asthe salt of sulfonic acid.

DESCRIPTION OF PREFERRED EMBODIMENTS

Preferably the mixture contains 2.7 to 7.3 wt. % sulfonated polysulfoneand 97.3-92.7 wt. % polysulfone.

According to the invention, synthetic membranes are preferred in whichthe product of the degree of sulfonation of the sulfonated polysulfoneand the percentage of sulfonated polysulfone in the mixture is ≦100,especially preferably ≦50.

Preferably the degree of sulfonation of the sulfonated polysulfone isbetween 0.5 and 15 mole-%, preferably however, between 2.5 and 9.0mole-%.

Preferably the polysulfones involved are mainly polyethersulfones.

Preferably the sulfonated polysulfones are mainly polyethersulfones.

Preferably the polysulfones contain as a structural unit, a group withthe formula: ##STR1##

Preferably the sulfonated polysulfones contain as a structural element agroup with the formula: ##STR2## where M=H, Li, Na, K, NH₄, 1/2 Mg, 1/2Ca.

The membrane according to the invention is sterilizable. Sterilizationcan be performed using hot steam or gamma radiation. However,sterilization can also be performed chemically if required.

According to the invention, the goal is also achieved of providing amethod for manufacturing a synthetic membrane characterized by the factthat one or more solvents are added to a mixture comprised of 0.5 to 8wt. % sulfonated polysulfone, possibly as the salt of the sulfonic acid,polysulfone, and not more than 20 wt. % of other polymers, the mixtureis dissolved to form a polymer solution, the latter is shaped, andprecipitated to form a membrane in a precipitating bath using one ormore precipitating agents.

In the design of the invention, the polymer solution, in addition to themixture of one or more polymers, such as polyvinylpyrrolidone, cancontain polyalkylene glycols such as polyethylene glycol, polypropyleneglycol, polyacrylic acids, or dextrans.

The precipitating agent is preferably a mixture of precipitating agentsand contains one or more non-solvents as well as solvents for themixture.

In addition, a gas or a mixture of gases that may contain solidparticles and/or liquid particles, can be used as the precipitatingagent.

According to a preferred embodiment of the invention, the gas is onethat is reactive with respect to the polymer solution.

In another embodiment of the invention, the gas is inert with respect tothe polymer solution.

Preferably dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone, ordimethylacetamide are used as the solvent.

In the design of the invention, additives that are soluble in thepolymer solution or the mixture of precipitating agents or are miscibletherewith, including water itself, are contained in the polymersolution.

Preferably the same solvent is used for the precipitating agent and inthe polymer solution.

Preferably the polymer solution is held at a temperature between 5° and95° C.

Preferably the temperature of the precipitating bath is held between 0°and 100° C.

Especially preferably the precipitating bath is held at a temperaturebetween 5° and 50° C.

According to one preferred embodiment of the invention, hollow fiberscan be produced with the polymer solution being shaped into a hollowfiber in a hollow fiber jet, with the internal cavity of the hollowfiber being formed by a mixture of one or more solvents with one or morenon-solvents.

In one preferred embodiment of the invention, the interior cavity isformed by a liquid.

According to another preferred embodiment of the invention, the innercavity of the hollow fiber is formed by means of gases, aerosols,vapors, or mixtures thereof to produce the hollow fibers.

In an embodiment of the invention, the precipitating agent with whichthe internal cavity is formed and the precipitating agent with which thehollow fiber is precipitated externally, have different compositions.

In one preferred embodiment of the invention, the spinnerette is locatedabove the precipitating bath and the distance between the spinneretteand the surface of the precipitating bath is at least 0.2 cm.

Another version according to the invention for manufacturing hollowfibers consists in the fact that the spinnerette is dipped in theprecipitating bath and the fiber is spun from top to bottom.

In an embodiment of the invention, the hollow fiber that is formed,after leaving the hollow fiber jet, spins at least 0.2 second in theprecipitating bath before it is deflected for the first time.

According to another preferred embodiment, the spinnerette is dipped inthe precipitating bath and the fiber is spun from bottom to top.

It has proven advantageous for the invention for the hollow fiber nozzleto have a temperature between 5° and 95° C.

However, according to the method described above, it is also possible tomake flat membranes or tubular membranes.

Preferably the membrane is washed and dried after leaving theprecipitating bath.

The invention will now be described in greater detail using thefollowing examples, in which PES stands for poly(ether)sulfone and SPESstands for sulfonated poly(ether)sulfone.

EXAMPLE 1

A spinning solution (polymer solution) composed of 22 wt. % of a mixtureof 7% wt. % SPES and 93 wt. % PES (Vitrex 5200) and 78 wt. %dimethylsulfoxide (DMSO) was extruded through a commercial annular gapnozzle whereby at the same time a solution composed of 20 wt. % DMSO, 70wt. % glycerin, and 10 wt. % H₂ O was added as an interior filling intothe internal cavity of the hollow fiber as it formed. The nozzle waslocated at a distance of 0.5 cm above the surface of the precipitatingbath. The temperature of the spinnerette was 60° C. The hollow fiber wasprecipitated in a precipitating bath with a composition of 90 wt. % DMSOand 10 wt. % H₂ O with the temperature of the precipitating bath being50° C. The hollow fiber was pulled out of the precipitating bath at arate of 60 m/min.

After washing the membrane with hot water at 60° C., aftertreatment wasperformed in a bath composed of 30 wt. % glycerin and 70 wt. %demineralized water. After winding and cutting, the material was driedat 113° C. for 45 minutes.

The resultant hollow fiber membrane had an inside diameter of 217 μm anda wall thickness of 24 μm.

The properties of the membrane were measured on bundles each composed of100 hollow fibers, with the hollow fibers being exposed to flowinternally in the permeability measurements.

An aqueous phosphate-buffered sodium chloride solution, containing 50 galbumin, 0.1 g cytochrome C, and 0.03 g sodium dithionite per liter ofsolution, was used to measure the ultrafiltration rate ofalbumin/cytochrome C solution.

The hollow fibers had the following properties:

    ______________________________________    Ultrafiltration rate with water:                         316 ml/(m.sup.2  · h · mmHg)    Ultrafiltration rate with albumin/                         55 ml/(m.sup.2  · h · mmHg)    cytochrome C solution:    Screening coefficient albumin:                         0.04    Screening coefficient cytochrome C:                         0.87    ______________________________________

In contrast to a comparable hollow fiber with a SPES content of morethan 70 wt. %, the hollow fiber according to the invention exhibitedbradykinin generation that was 82% less.

EXAMPLE 2

The method described in Example 1 was repeated, but the internal fillingconsisted of 20 wt. % DMSO, 65 wt. % glycerin, and 15 wt. % water.

The temperature of the precipitating bath was 25° C.; all the otherparameters were the same as in Example 1.

The membrane hollow fibers thus obtained had an inside diameter of 209μm and a wall thickness of 24 μm.

The following performance data were measured on the hollow fibers:

    ______________________________________    Ultrafiltration rate with water:                          278 ml/(m.sup.2  · h · mmHg)    Ultrafiltration rate with albumin/                          43 ml/(m.sup.2  · h · mmHg)    cytochrome C solution:    Screening coefficient albumin:                          0.02    Screening coefficient cytochrome C:                          0.77    Dialytic permeability for vitamin B12:                          7.2 × 10.sup.-3  cm/min    Dialytic permeability for creatinine:                          21.9 × 10.sup.-3  cm/min    ______________________________________

EXAMPLE 3

The method described in Example 2 was repeated, using a solution withthe composition 40 wt. % DMSO, 40 wt. % glycerin, and 20 wt. % water tofill the interior.

The resultant membrane hollow fibers had a lumen measuring 209 μm and awall thickness of 23 μm.

The following performance data were measured on them:

    ______________________________________    Ultrafiltration rate with water:                          337 ml/(m.sup.2  · h · mmHg)    Ultrafiltration rate with albumin/                          35 ml/(m.sup.2  · h · mmHg)    cytochrome C solution:    Screening coefficient albumin:                          0.00    Screening coefficient cytochrome C:                          0.27    Dialytic permeability for vitamin B12:                          11.7 × 10.sup.-3  cm/min    Dialytic permeability for creatinine:                          34.4 × 10.sup.-3  cm/min    ______________________________________

EXAMPLE 4

The method described in Example 2 was repeated but the interior fillingconsisted of 30 wt. % DMSO, 60 wt. % glycerin, and 10 wt. % water.

The hollow fiber thus obtained had an inside diameter of 204 μm and awall thickness of 20 μm.

It had the following properties:

    ______________________________________    Ultrafiltration rate with water:                          253 ml/(m.sup.2  · h · mmHg)    Ultrafiltration rate with albumin/                          43 ml/(m.sup.2  · h · mmHg)    cytochrome C solution:    Screening coefficient albumin:                          0.03    Screening coefficient cytochrome C:                          0.80    Dialytic permeability for vitamin B12:                          12.5 × 10.sup.-3  cm/min    Dialytic permeability for creatinine:                          38.2 × 10.sup.-3  cm/min    ______________________________________

EXAMPLE 5

The same procedure was used as in Example 1, but the spinning solutionconsisted of 21 wt. % of a mixture of 7 wt. % SPES and 93 wt. % PES and79 wt. % DMSO; the interior filling consisted of 40 wt. % DMSO, 50 wt. %glycerin, and 10 wt. % water.

The hollow fiber exhibited the following properties:

    ______________________________________    Inside diameter:      210 μm    Wall thickness:       22 μm    Ultrafiltration rate with water:                          230 ml/(m.sup.2  · h · mmHg)    Ultrafiltration rate with albumin/                          40 ml/(m.sup.2  · h · mmHg)    cytochrome C solution:    Screening coefficient albumin:                          0.02    Screening coefficient cytochrome C:                          0.80    Dialytic permeability for vitamin B12:                          9.0 × 10.sup.-3  cm/min    Dialytic permeability for creatinine:                          27.5 × 10.sup.-3  cm/min    ______________________________________

EXAMPLE 6

The same method was used as in Example 1 but the spinning solutionconsisted of 21 wt. % of the mixture of 7 wt. % SPES and 93 wt. % PES(Ultrason E 6020 P), 3 wt. % water, and 76 wt. % DMSO, while theinterior filling was composed of 35 wt. % DMSO, 50 wt. % glycerin, and15 wt. % water.

The temperature of the spinnerette was 70° C. The spinnerette was dippedin the precipitating bath and the fiber spun from top to bottom. Thetemperature of the precipitating bath was 15° C. Then an aftertreatmentbath composed of 50 wt. % glycerin and 50 wt. % water was applied to thehollow fiber using suitable nozzles.

The hollow fiber had the following properties:

    ______________________________________    Inside diameter:      204 μm    Wall thickness:       19 μm    Ultrafiltration rate with water:                          226 ml/(m.sup.2  · h · mmHg)    Ultrafiltration rate with albumin/                          48 ml/(m.sup.2  · h · mmHg)    cytochrome C solution:    Screening coefficient albumin:                          0.001    Screening coefficient cytochrome C:                          0.43    Dialytic permeability for vitamin B12:                          13.8 × 10.sup.-3  cm/min    Dialytic permeability for creatinine:                          43.5 × 10.sup.-3  cm/min    ______________________________________

EXAMPLE 7

The procedure was the same as in Example 6 but the interior fillingconsisted of 33.6 wt. % DMSO, 48 wt. % glycerin, 14.4 wt. % water, and 4wt. % polyvinylpyrrolidone.

The hollow fiber thus produced had the following properties:

    ______________________________________    Inside diameter:      210 μm    Wall thickness:       22 μm    Ultrafiltration rate with water:                          206 ml/(m.sup.2  · h · mmHg)    Ultrafiltration rate with albumin/                          54 ml/(m.sup.2  · h · mmHg)    cytochrome C solution:    Screening coefficient albumin:                          0.002    Screening coefficient cytochrome C:                          0.34    Dialytic permeability for vitamin B12:                          14.3 × 10.sup.-3  cm/min    Dialytic permeability for creatinine:                          46.6 × 10.sup.-3  cm/min    ______________________________________

EXAMPLE 8

The procedure was the same as in Example 6 but the spinning solutionconsisted of 23 wt. % of a mixture of 7 wt. % SPES and 93 wt. % PES, 3wt. % water,and 74 wt. % DMSO, while the interior filling consisted of88 wt. % glycerin and 12 wt. % water.

The hollow fiber thus produced had the following properties:

    ______________________________________    Inside diameter:      192 μm    Wall thickness:       35 μm    Ultrafiltration rate with water:                          150 ml/(m.sup.2  · h · mmHg)    Ultrafiltration rate with albumin/                          43 ml/(m.sup.2  · h · mmHg)    cytochrome C solution:    Screening coefficient albumin:                          0.004    Screening coefficient cytochrome C:                          0.19    Dialytic permeability for vitamin B12:                          8.2 × 10.sup.-3  cm/min    Dialytic permeability for creatinine:                          26.0 × 10.sup.-3  cm/min    ______________________________________

EXAMPLE 9

The procedure was the same as in Example 8 but the hollow fiber wasstretched in a water bath at 60° C. by 20% and then relaxed 2.8%.

The hollow fiber exhibited the following properties:

    ______________________________________    Inside diameter:      192 μm    Wall thickness:       34 μm    Ultrafiltration rate with water:                          370 ml/(m.sup.2  · h · mmHg)    Ultrafiltration rate with albumin/                          68 ml/(m.sup.2  · h · mmHg)    cytochrome C solution:    Screening coefficient albumin:                          0.052    Screening coefficient cytochrome C:                          0.72    Dialytic permeability for vitamin B12:                          11.3 × 10.sup.-3  cm/min    Dialytic permeability for creatinine:                          34.5 × 10.sup.-3  cm/min    ______________________________________

All the hollow fibers according to the invention exhibit a significantlyreduced histamine release and bradykinin generation in contrast tocorresponding hollow fibers like those that can be produced according tothe known prior art, for example, with a content of more than 70% SPES.

While the invention has been described in detail and with reference tospecific examples thereof, it will be apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A synthetic hemodialysis membrane comprisingpolyethersulfone and 0.5 to 8 wt. % sulfonated polyethersulfone, whereinsaid sulfonated polyethersulfone has a degree of sulfonation of between0.5 and 9.0 mole-%, and wherein the polyethersulfone comprises a groupwith the formula: ##STR3##
 2. The synthetic hemodialysis membraneaccording to claim 1, wherein said sulfonated polyethersulfone is a saltof a sulfonic acid.
 3. The synthetic hemodialysis membrane according toclaim 1, comprising 2.7 to 7.3 wt. % of said sulfonated polyethersulfoneand 97.3 to 92.7 wt. % of said polyethersulfone.
 4. The synthetichemodialysis membrane according to claim 1, wherein said sulfonatedpolyethersulfone has a degree of sulfonation which when multiplied bythe wt. % of sulfonated polyethersulfone yields a product ≦50.
 5. Thesynthetic hemodialysis membrane according to claim 1, wherein saidsulfonated polysulfone has a degree of sulfonation which is between 2.5and 9.0 mole-%.
 6. The synthetic hemodialysis membrane according toclaim 1, further comprising at least one other polymer selected from thegroup consisting of polyethylene glycol, polypropylene glycol,polyacrylic acids, dextran and polyvinylpyrrolidone.
 7. The synthetichemodialysis membrane according to claim 1, wherein the sulfonatedpolysulfone comprises a group with the formula: ##STR4## where M is H,Li, Na, K, NH₄, 1/2 Mg or 1/2 Ca.
 8. The synthetic hemodialysis membraneaccording to claim 1, wherein said membrane is sterilizable.
 9. Thesynthetic hemodialysis membrane according to claim 8, wherein saidmembrane is sterilizable by hot steam or gamma radiation.
 10. A methodfor manufacturing a synthetic hemodialysis membrane, said methodcomprising:mixing 0.5 to 8 wt. % sulfonated polyethersulfone andpolyethersulfone to form a mixture, said polyethersulfone comprising agroup with the formula: ##STR5## and said sulfonated polyethersulfonehas a degree of sulfonation of between 0.5 and 9.0 mole-%; dissolvingsaid mixture in at least one solvent to form a polymer solution; shapingsaid polymer solution; and precipitating said polymer solution in aprecipitating bath comprising at least one precipitating agent to formsaid synthetic hemodialysis membrane.
 11. The method according to claim10, wherein said sulfonated polyethersulfone is a salt of a sulfonicacid.
 12. The method according to claim 10, wherein the polymer solutionfurther comprises a polyalkylene glycol.
 13. The method according toclaim 10, wherein said polymer solution further comprises at least onepolymer selected from the group consisting of polyethylene glycol,polypropylene glycol, polyacrylic acids, dextran andpolyvinylpyrrolidone.
 14. The method according to claim 10, wherein theprecipitating bath comprises a plurality of precipitating agents and atleast one non-solvent for the mixture.
 15. The method according to claim14, wherein the precipitating bath further comprises at least oneprecipitating agent solvent for the mixture.
 16. The method according toclaim 15, wherein the solvent is the same as the precipitating agentsolvent.
 17. The method according to claim 10, wherein said at least oneprecipitating agent comprises at least one gas.
 18. The method accordingto claim 17, wherein said at least one precipitating agent furthercomprises at least one member selected from the group consisting ofsolid particles and liquid particles.
 19. The method according to claim17, wherein said at least one gas is reactive with respect to thepolymer solution.
 20. The method according to claim 17, wherein said atleast one gas is inert with respect to the polymer solution.
 21. Themethod according to claim 10, wherein said at least one solvent isselected from the group consisting of dimethylformamide,dimethylsulfoxide, N-methylpyrrolidone and dimethylacetamide.
 22. Themethod according to claim 10, wherein at least one of said polymersolution and said precipitating agent comprises at least one additivethat is soluble in or miscible with the polymer solution or theprecipitating agent, respectively.
 23. The method according to claim 22,wherein said at least one additive is water.
 24. The method according toclaim 10, wherein the polymer solution is maintained at a temperaturebetween 5° and 95° C.
 25. The method according to claim 10, wherein theprecipitating agent is maintained at a temperature between 0° and 100°C.
 26. The method according to claim 10, wherein the precipitating agentis maintained at a temperature between 5° and 50° C.
 27. The methodaccording to claim 10, wherein the polymer solution is shaped in ahollow fiber nozzle to form a hollow fiber with a continuous interiorcavity, the interior cavity of the hollow fiber being formed by at leastone shaping solvent and at least one non-solvent.
 28. The methodaccording to claim 27, wherein the interior cavity is formed by aliquid.
 29. The method according to claim 27, wherein the interiorcavity is formed by at least one member selected from the groupconsisting of gases, aerosols and vapors.
 30. The method according toclaim 27, wherein the interior cavity is formed by a cavity-formingprecipitating agent having a different composition from a fiber-formingprecipitating agent that forms the hollow fiber.
 31. The methodaccording to claim 27, wherein the hollow fiber nozzle is located abovethe precipitating bath and a distance between the hollow fiber nozzleand the precipitating bath surface is at least 0.2 cm.
 32. The methodaccording to claim 27, wherein the hollow fiber nozzle dips into theprecipitating bath and the fiber is spun from top to bottom.
 33. Themethod according to claim 27, wherein the hollow fiber formed, afterleaving the hollow fiber nozzle, spends at least 0.2 seconds in theprecipitating bath before it is deflected for the first time.
 34. Themethod according to claim 27, wherein the hollow fiber nozzle dips intothe precipitating bath and the hollow fiber is spun from bottom to top.35. The method according to claim 27, wherein the hollow fiber nozzlehas a temperature between 5° and 95° C.
 36. The method according toclaim 10, wherein said synthetic hemodialysis membrane is flat ortubular.
 37. The method according to claim 10, further comprisingremoving said synthetic hemodialysis membrane from the precipitatingbath, and subsequently washing and drying the synthetic hemodialysismembrane.